Helical antenna scanning system



Dec. 22, 1953 M. D. ADCOCK ET AL 2,663,369

HELICAL. ANTENNA SCANNING SYSTEM Filed July 7, 1950 3mm v MACK DONALD ADCOCK I ARTHUR -EMARSTON ATTORN EYS Patented Dec. .22, 1953 HELHJAL ANTENNA SCANNING SYSTEM Mack Donald Adcock and Arthur E. Marston, Washington, D. 0.

Application July 7, 1950, Serial No. 172,582

4 Claims.

(Granted under rule 35, U. s. Code (1952),

see. 266) This invention relates in general to antenna arrays providing directional beams to electromagnetic energy, and particularly to a helical antenna array in which the radiating or reception pattern is periodically varied or scanned.

In conventional antenna systems, it is frequently desirable to provide a highly directive beamcr pattern of electromagnetic energy, that is, with maximum gain in a. specific direction. It is also desirable, in many instances, to obtain as broad an area of coverage as possible in addition to maintaining a more or less specific directivity. However to obtain the one usually signifies a sacrifice of the other.

There are known antenna systems in the art wherein a highly directive beam pattern is varied periodically or permitted to oscillate in a scanning manner. With this method there can be obtained a highly directive beam pattern that has an efiective reasonably broad area of coverage. These systems may generally be classed into one of two groups. In the first group there are those that depend entirely on mechanical means to rotate or oscillate the pattern-producing device, uch as by oscillating a directional reflector. In the second group of varying beam scanners there may be classed those systems which are entirely electrical, such as varying the phase of the currents energizing the antennas.

The mechanical systems, as a rule, are generally bulky and cumbersome and require a complexity of apparatus. The electrical systems are equally bulky and complex requiring a number of phase delay networks, phase shifters and/r swinging frequency oscillators.

The present invention is an antenna system employing a plurality of helical elements which provide a highly directive pattern. The directive pattern is periodically permitted to oscillate as a scanner, as described hereinafter, by a simple combination of mechanical and electrical means, generally overcoming the disadvantages of each.

It is accordingly an object of the present invention to provide a new and improved antenna array.

It is a further object of the present invention to provide a circularly polarized antenna array offering a highly directive radiation and/or reception pattern.

It is another object of the present invention to provide an antenna array employing a plurality of helical elements adapted to give a highly directive radiation and/or reception pattern and further ofiering a reasonably broad area of coverage.

their longitudinal axes.

Another object of the present invention is to provide an improved directional antenna array employing a plurality of helical elements having a Variable directional characteristic.

Still another object of the present invention is to provide an antenna array employing a plurality of helical elements in which the elements are rotated to periodically vary the relative phase between the elements for producing thereby an oscillating directional characteristic.

Further objects and attainments of the present invention will become apparent from the following detailed description when taken in conjunction with the drawings in which:

Fig. 1 is a typical illustration of a preferred embodiment of the present invention.

Fig. 2 shows generally the antenna pattern obtainable with the preferred embodiment intended to illustrate one feature of the present invention.

The antenna array constructed in accordance with the teachings of the present invention employs a plurality of similar helical antenna ele ments. The helical elements in the preferred embodiment are of the filament (end-fire) type at the particular frequency at which they are designed for operation, that is, at the desired frequency the radiation is maximum in the direction along the longitudinal axis of the helices. The polarization of the antennas comprising the array when used for reception as well as transmission, is substantially circular. The helical antennas are symmetrically disposed, with respect to a suitable reference point and are connected to transmission lines in parallel to provide currents of equal phase.

We have discovered a unique property of the helical antenna that, when incorporated in an antenna array, provides the basis of the present invention. This unique property relates more specifically to the phasing of the helices, with respect to each other, which may be controlled by the angular orientation of the helices about The phase of the radiation field of the helices is reflected by the angular orientation distinction therebetween. As an example, if it is desired to have a phase difference of between four helical elements, the first or the four helical antennas would be oriented at 0, the second antenna would be oriented so that the first turn subtends a 90 angle with respect to the first helix, the third a angle with respect to the first and the fourth at 270 angle with respect to the first.

Referring now in particular to Fig. 1 there is shown, by way of illustration only, a side view of an helical antenna array scanning system designed to give maximum gain in a specific direction and to cover a reasonably broad area. The principle of operation of the scanning antenna array is predicated upon the phasing principle hereintofore described.

In operation of the scanning system, the helical antennas are of a sufficient number of turns to focus its gain in a specific direction, the area of coverage of the helices or their directivity is of course dependent on the number of turns of each helix. To obtain a broad area of coverage at least one of the helices is rotated about its longitudinal axis to give a varying phase difference between helices, thereby shifting the antenna pattern back and forth from a single main lobe.

to a pair of divergent overlapping lobes and back again to a single main lobe in a scanning manner. There is illustrated, more specifically in l, a helical antenna array comprising two helical elf. ments I and 2. It is to be understood that the number of helices shown is for purposes of illustration and any number of helices may be employed in an array in accordance with the principles of the present invention. The two helices l and 2 are symmetrically disposed, with respect to a central point above ground plane .29 and are energized in phase with transmission lines connested in parallel, shown fragmentarily at 3 and Helix l has associated therewith, means for rotating the helix about its longitudinal axis. The means shown is, of course, merely illustrative and any means known to those skilled in the art may readily be substituted. The outer conductor 21 of transmission line is rotatably terminated in ground plane 29 through bearings 23. Also fitted around the outer conductor 25 is bevel gear 23 which is positioned to mesh with gear 8! driven by the motor drive 25. Rotary joint 25 may be a capacitive type rotary joint, or any conventional rotary joint, for purposes of passing R. F. to the antenna.

In conformance with the phasing principle described above, when the first turns, !3 of helix l and it of helix 2, have an identical radial direction such as shown in Fig. 1 they are in phase. If helix 1 were rotated so that the first turn l3 subtends 45, with respect to helix 2, there would be a 45 phase difference between the two helices. By having an electrical motor driven arrangement as illustrated in the drawings, to provide a rapid rotating motion of helix 4, the directional field pattern is caused to vary or scan con-.

tinuously from a single main lobe to a pair of divergent overlapping lobes and back again by providing a periodically varying phase shift for the antenna elements.

With reference to Fig. 2 there is illustrated, typically, the different angular positions the field pattern may assume by varying the phase of the elements as described above. When the two helical antennas are in phase, 1. e., oriented in the same direction, the radiant energy pattern transmitted thereby will have the orientation indicated by the single main lobe Ill, having its directivity axis substantially parallel to the axis of the antenna elements. If the antenna elements are not in phase, that is, one of the elements is rotated with respect to the other, the directivity pattern h] will become such as shown H-H or i2--l2 depending upon the relative angular orientation of the elements. Ihe degree 4 of the shift will be proportional to the magnitude of the phase displacement or rotation.

More particularly when helix l is rotated for example, the phase variation of 90 which exists between helix 1 and helix 2 will displace the single main lobe pattern it} away in either direction from the normal axis of directivity of the array to substantially that shown by the di vergent overlapping dotted line pattern Hl|. When the helix l is rotated the phase deviation of 180 which exists, between helix l and helix 2, will displace the single main lobe pattern l0v from the normal axis of directivity of the array in either direction as indicated by the divergent overlapping dotted line pattern l2--l2. A rotation of 270 of one of the helices will return the pattern back to that shown at li-l l, since there would only be a 90 relative phase difference between helices. It is seen then that by imparting a rapid rotating motion to at least one of the antenna elements the pattern may be swept back and forth from a single main lobe to a pair of divergent overlapping lobes and back again to cover an effective area as shown between the outer lines of the two dotted line patterns l2-l2.

It may be more advantageous in certain in-- stances to rotate both antennas rather than a single antenna. That is, rather than continuously rotate, for instance, helix 5 from 0 through 360, it may be preferable to rotate both elements simultaneously in the same or in opposite directions. Any suitable mechanical linkage such as a mechanical differential coupling between the two helices may be used to accomplish this type control.

In certain instances it may be more feasible to energize the antennas out of phase rather than in phase as indicated above. The present system lends itself equally as well applicable by a preliminary adjustment of the orientation of the helices by an amount in proportion to their phase displacement. The helices then would be in phase and the same scanning procedure would be carried out.

Although certain specific embodiments of this invention have been disclosed and described it is to be understood that they are merely illustrative of this invention and modifications may, of course, be. made without departing from the spirit and scope of the invention.

The. invention described herein may be mama factured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A helical antenna scanning system comprising: a plurality of similar helical elements, the longitudinal axes of said helical elements being laterally displaced and positioned in mutual parallelism and means for continuously rotating at least one of said elements about its longitudinal axisto continuously vary the relative turn orientation of said helical elements about said axes thereby reciprocally broadening and narrowing the area of coverage of said helical antenna.

2. An antenna array comprising a plurality of helically wound antenna elements each having a turn pitch and diameter to produce substantially circularly polarized radiation at the operating frequency thereof, the axes of said helical elements being laterally displaced, and means for varying the relative turn orientation of said elements about said axes.

3. An antenna array comprising a ground plane for said array, a plurality of helically wound radiator elements each having a turn pitch and diameter to produce substantially circularly polarized radiation at the operating frequency thereof, the axes of said helical elements being laterally displaced and symmetrically disposed about a point on said ground plane, and means for varying the relative turn orientation of said elements about said axes.

4. An antenna array comprising a ground plane for said array, a plurality of helically wound radiator elements each having a turn pitch and diameter to produce substantially circularly polarized radiation at the operating frequency thereof, said helical elements having laterally displaced axes and being symmetrically disposed about a central point on said ground plane, transmission lines connecting said elements in parallel for energizing said elements in phase, and means for varying the relative turn orientation of said elements about said axes.

MACK DONALD ADCOCK. ARTHUR E. MARSTON.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES The Helical Antenna by John D. Kraus, Free. I. R. E., vol. 37, No. 3, March 1949, pages 263 to 272.

"Helical Beam Antenna by John D. Kraus, Electronics, April 1947, pages 109 to 111. 

